1. Field of the Invention
The present invention relates to an electrolytic capacitor, and particularly to an electrolytic capacitor formed by winding an anode foil, a cathode foil and the like.
2. Description of the Background Art
An electrolytic capacitor formed by winding up an anode foil and a cathode foil with separator paper being interposed represents one form of an electrolytic capacitor.
Here, a method of manufacturing an electrolytic capacitor having a two-terminal (one anode terminal and one cathode terminal) structure representing such a wound-type electrolytic capacitor will now be described. Initially, as shown in FIG. 52, band-shaped anode foil 103 and cathode foil 104 each having a prescribed length and two sheets of separator paper 105, 106 are prepared. For example, an aluminum foil having a dielectric oxide film formed is applied as an anode foil and an aluminum foil is applied as a cathode foil.
An anode lead tab terminal 110 is connected at a prescribed position in a longitudinal direction of anode foil 103, and a cathode lead tab terminal 113 is connected at a prescribed position in a longitudinal direction of cathode foil 104. As shown in FIGS. 53 and 54, a columnar boss portion 116a, a plate-shaped connection portion 116b connected to anode foil (cathode) 103, 104, and a columnar lead 116c serving as an anode (a cathode) terminal are provided in anode (cathode) lead tab terminal 110, 113.
As shown in FIG. 52, anode foil 103, cathode foil 104 and the like are arranged in such a manner that one sheet of separator paper 105 is sandwiched between anode foil 103 and cathode foil 104 and anode foil 103 is sandwiched between one sheet of separator paper 105 and the other sheet of separator paper 106.
Then, as shown in FIG. 55, one-end sides of arranged anode foil 103, cathode foil 104 and sheets of separator paper 105, 106 are sandwiched between cores 131a and 131b. Then, by turning cores 131a, 131b clockwise in that state, anode foil 103, cathode foil 104 and the like are wound up from the one-end side, to thereby form a wound-type electrolytic capacitor.
An electrolytic capacitor has an inductance component referred to as equivalent series inductance (ESL). This ESL increases with the increase in a frequency, and then the electrolytic capacitor cannot function as a capacitor. Therefore, an electrolytic capacitor used in a high-frequency region is required to have lower ESL. In addition, an electrolytic capacitor has a resistance component referred to as equivalent series resistance (ESR), and it is required to have lower ESR.
In order to lower ESR and ESL, a multi-terminal electrolytic capacitor including a plurality of lead tab terminals as lead tab terminals is available. A method of manufacturing an electrolytic capacitor having a four-terminal (two anode terminals and two cathode terminals) structure representing such a multi-terminal electrolytic capacitor will now be described.
As shown in FIG. 56, a first anode lead tab terminal 111 and a second anode lead tab terminal 112 are connected at prescribed positions in a longitudinal direction of anode foil 103 respectively, and a first cathode lead tab terminal 114 and a second cathode lead tab terminal 115 are connected at prescribed positions in a longitudinal direction of cathode foil 104 respectively. Anode foil 103, cathode foil 104 and the like are arranged as in the case of a two-terminal electrolytic capacitor, and one-end sides thereof are sandwiched between cores 131a and 131b (see FIG. 55). By turning cores 131a, 131b clockwise in that state, anode foil 103, cathode foil 104 and the like are wound up from the one-end side, to thereby form a capacitor element 102 as shown in FIG. 57.
Then, a cut surface or the like of anode foil 103 and cathode foil 104 of capacitor element 102 is subjected to a prescribed treatment such as chemical conversion treatment. Then, a sealing rubber gasket 122 (see FIG. 58) is attached to capacitor element 102. In sealing rubber gasket 122, four openings 122a (see FIG. 58) corresponding to positions of respective lead tab terminals 111, 112, 114, 115 are formed. Sealing rubber gasket 122 is attached to capacitor element 102 such that leads 116c of lead tab terminals 111, 112, 114, 115 are inserted in respective openings 122a. 
Capacitor element 102 to which sealing rubber gasket 122 is attached is accommodated in an aluminum case 120 with a bottom (see FIG. 58) having a prescribed size. Then, an open-end side of aluminum case 120 is sealed by pressing in a lateral direction and curling and prescribed aging treatment is performed. Then, a seat plate 124 made of plastic is attached to a curled surface of aluminum case 120. Four openings 124a (see FIG. 58) corresponding to positions of respective lead tab terminals 111, 112, 114, 115 are formed in seat plate 124.
Thereafter, as shown in FIG. 58, each lead 116c protruding through opening 124a in seat plate 124 and serving as an electrode terminal is pressed and bent, to thereby complete an electrolytic capacitor 101 having a four-terminal structure.
A method of manufacturing an electrolytic capacitor having a three-terminal (two anode terminals and one cathode terminal) as a multi-terminal electrolytic capacitor will now be described.
As shown in FIG. 59, first anode lead tab terminal 111 and second anode lead tab terminal 112 are connected at prescribed positions in a longitudinal direction of anode foil 103 respectively, and cathode lead tab terminal 113 is connected at a prescribed position in a longitudinal direction of cathode foil 104. Anode foil 103, cathode foil 104 and the like are arranged as in the case of a two-terminal electrolytic capacitor, and one-end sides thereof are sandwiched between cores 131a and 131b (see FIG. 55). By turning cores 131a, 131b clockwise in that state, anode foil 103, cathode foil 104 and the like are wound up from the one-end side, to thereby form capacitor element 102 as shown in FIG. 60.
Then, a cut surface or the like of anode foil 103 and cathode foil 104 of capacitor element 102 is subjected to a prescribed treatment such as chemical conversion treatment. Then, sealing rubber gasket 122 (see FIG. 61) is attached to capacitor element 102. In sealing rubber gasket 122, three openings 122a (see FIG. 61) corresponding to positions of respective lead tab terminals 111, 112, 113 are formed. Sealing rubber gasket 122 is attached to capacitor element 102 such that leads 116c of lead tab terminals 111, 112, 113 are inserted in respective openings 122a. 
Capacitor element 102 to which sealing rubber gasket 122 is attached is accommodated in aluminum case 120 with a bottom (see FIG. 61) having a prescribed size. Then, an open-end side of aluminum case 120 is sealed by pressing in a lateral direction and curling and prescribed aging treatment is performed. Then, seat plate 124 made of plastic is attached to a curled surface of aluminum case 120. Three openings 124a (see FIG. 61) corresponding to positions of respective lead tab terminals 111, 112, 113 are formed in seat plate 124.
Thereafter, as shown in FIG. 61, each lead 116c protruding through opening 124a in seat plate 124 and serving as an electrode terminal is pressed and bent, to thereby complete electrolytic capacitor 101 having a three-terminal structure.
It is noted that Patent Document 1 (Japanese Patent Laying-Open No. 2004-179621) is an exemplary document disclosing an electrolytic capacitor having a multi-terminal structure such as a two- to four-terminal structure.
The inventors, however, have found that a conventional electrolytic capacitor having a multi-terminal structure suffers the following problems.
As described above, an electrolytic capacitor used in a high-frequency region in particular is required to have lower ESL. Since this ESL depends on a pitch between leads of anode (cathode) lead tab terminals, in order to lower ESL, the anode (cathode) lead tab terminals should be arranged in good balance, with regular pitches between the leads being set.
Namely, in the case of an electrolytic capacitor having a four-terminal structure, when electrolytic capacitor 101 is viewed from the anode (cathode) lead tab terminal side, it is required that first anode lead tab terminal 111, second anode lead tab terminal 112, first cathode lead tab terminal 114, and second cathode lead tab terminal 115 are arranged at positions corresponding to respective vertices of a square (or a rectangle).
Here, as shown in FIG. 62, it is assumed that two anode lead tab terminals 111, 112 are arranged in one anode foil 103 at positions corresponding to respective vertices of a square after winding-up. Then, as an electrolytic capacitor has a smaller diameter, a distance PL between two anode lead tab terminals 111 and 112 becomes shorter. For example, in an electrolytic capacitor having a diameter of 6.3 mm, distance PL between two anode lead tab terminals 111 and 112 should be set to several mm.
In the electrolytic capacitor having a diameter of 6.3 mm, however, a length L of anode foil 103 is around 60 to 70 mm, and it is difficult to accurately connect two anode lead tab terminals 111, 112 to anode foil 103 having such a length L at an interval of several mm (distance PL).
Meanwhile, in order to lower ESR, an anode lead tab terminal is desirably connected to an anode foil such that a resistance value of a portion of the anode foil extending toward one side with respect to an anode lead tab terminal connected to the anode foil is equal to a resistance value of a portion of the anode foil extending toward the other side.
Namely, the two anode lead tab terminals are desirably arranged such that a distance half the interval therebetween (distance PL), that is, a distance between one end of the anode foil and the anode lead tab terminal closest thereto is substantially equal to a distance between the other end of the anode foil and the anode lead tab terminal closest thereto. Therefore, if two anode lead tab terminals are connected to one anode foil too closely to each other, such a situation is the same as a state that substantially one anode lead tab terminal is connected, and characteristics as an electrolytic capacitor will be interfered in particular in a high-frequency region.
In order to overcome such disadvantages, the inventors made the following evaluation in order to ensure an interval between two anode lead tab terminals. Initially, in a state that an anode foil and the like are wound up, a position in a circumferential direction where a first anode lead tab terminal is arranged is defined as a first position in a circumferential direction, and a position in a circumferential direction where a second anode lead tab terminal is arranged is defined as a second position in a circumferential direction.
As shown in FIG. 63, anode foil 103, in which interval PL between first anode lead tab terminal 111 and second anode lead tab terminal 112 is set to an interval between a portion of anode foil 103 corresponding to the first position in the circumferential direction and a portion of anode foil 103 corresponding to the second position in the circumferential direction after winding up a closest portion of anode foil 103 corresponding to the second position in the circumferential direction with respect to the first position in the circumferential direction, and further winding up again anode foil 103, was prepared as anode foil 103.
Based on evaluation of winding-up using this anode foil 103 and the like, as shown in FIG. 64, a new problem that a position in a radial direction of second anode lead tab terminal 112 is displaced from a position in a radial direction of first anode lead tab terminal 111 was found to arise. It is noted that a case where a position in a radial direction of second anode lead tab terminal 112 is in registration with a position in a radial direction of first anode lead tab terminal 111, that is, a case where anode (cathode) lead tab terminals are arranged in good balance with pitches between four leads 116c being equal to each other, is shown in FIG. 64 with a dotted line.
As described above, in a wound-type electrolytic capacitor, one-end sides of the anode foil, the cathode foil and two sheets of separator paper are sandwiched between the cores, and they are wound up from the one-end side in that state. Therefore, in second winding and later, the anode foil and the like are further wound up over the portion of the anode foil and the like wound up so far.
Then, even if a position in a circumferential direction is the same, a portion wound up in an early stage is different in position in a radial direction from a portion wound up in a final stage, and thus a distance in a radial direction from a point of start of winding (center) becomes greater in a later stage of winding-up. Therefore, as shown in FIG. 64, regarding a circumferential direction, though second anode lead tab terminal 112 is arranged at a prescribed second position in a circumferential direction with respect to the first position in the circumferential direction where first anode lead tab terminal 111 is arranged, regarding a radial direction, it is arranged on an outer side relative to the position in the radial direction in a case where connection to the closest portion of anode foil 103 corresponding to the second position in the circumferential direction with respect to the first position in the circumferential direction. Namely, second anode lead tab terminal 112 is arranged on the outer side relative to the position in the radial direction of first anode lead tab terminal 111.
This is also the case with the first cathode lead tab terminal and the second cathode lead tab terminal, and in capacitor element 102 formed by winding up the anode foil and the like, two anode lead tab terminals 111, 112 and two cathode lead tab terminals 114, 115 are not arranged at positions corresponding to respective vertices of a square.
If two anode lead tab terminals 111, 112 and two cathode lead tab terminals 114, 115 are displaced from the positions corresponding to the respective vertices of the square, pitches between anode (cathode) lead tab terminals 111, 112, 114, 115 vary, ESL increases, and characteristics as the electrolytic capacitor become poorer. In addition, it becomes difficult to insert each anode (cathode) lead tab terminal 111, 112, 114, 115 in opening 122a in sealing rubber gasket 122 or opening 124a in seat plate 124 and productivity is interfered.
This is also the case with an electrolytic capacitor having a three-terminal structure. As shown in FIG. 65, in capacitor element 102 formed by winding up the anode foil and the like, two anode lead tab terminals 111, 112 and cathode lead tab terminal 113 are not arranged at positions corresponding to respective vertices of an equilateral triangle.
If two anode lead tab terminals 111, 112 are displaced from positions corresponding to respective vertices of an equilateral triangle, pitches between anode (cathode) lead tab terminals 111, 112, 113 vary, ESL increases, and characteristics as the electrolytic capacitor become poorer. In addition, it becomes difficult to insert each anode (cathode) lead tab terminal 111, 112, 113 in opening 122a in sealing rubber gasket 122 or opening 124a in seat plate 124 and productivity is interfered.